DTap titer to check for immunity from partial vax?

[beebalmmama]

So we are non-vax for the most part. Except opted to get DTap for ds 1 when he was 2.5 yrs. He seemed pretty suceptible to horrible coughs with most colds and so we thought it would be best. He has had (I believe, I can't find his records at the moment) 3 out of the 4 required doses, based on the schedule of first dose after 2 yrs. I'm not sure of the exact dose numbers here, but I know he was due for one more for a full vax. I've been hesitant to give him this last one.....I don't really know why. Maybe because now that ds 2 is here (15 months) I'm concerned about bringing anything around him..... Also you hear others experiences of later doses of a vax still having really bad side effects. 

So I was wondering if there is a titer/test to check for immunity for DTap and how accurate it might be. I'd like to at least see before we opt for another dose if necessary. I should mention that at this point I'm not really concerned about the Pertussis protection because he seems to have grown out of the cough issues but it would be nice to know he has the Diptheria and Tetnus protection. 

[Marnica]

There is a titer test for all three

 If your doc won't do them - you can get them here without a rx

http://drtenpenny.com/titer.aspx

If you discover that the titers are unaccptable for tetanus and Diptheria, (and you don't want or care about the pertussis component) I believe you can get the last dose at the Td rather than the DTaP.